The present invention relates to an apparatus for forming thin films on substrates, processing thin films formed on substrates and removing contaminants and oxidized films from processed substrates in fabricating electronic, including semiconductor integrated circuits, liquid crystal displays and printed wiring boards, and, more particularly, to a plasma processing method and a plasma processing apparatus capable of producing a high-density plasma in a low-pressure region, of controlling the amount and energy of ions incident on a processed substrate and of forming a uniform plasma in a wide area to process a substrate having a large area uniformly and quickly without damaging the substrate by the plasma.
Plasma processing apparatuses and plasma processing methods employing microwaves are disclosed in Japanese Patent Application Laid-open (Kokai) Nos. 51-71593, 52-126175, 53-96938 and 56-155535.
These prior art plasma processing methods produce a high-density plasma by causing electron cyclotron resonance by the combination of a microwave and a static magnetic field. Generally, these methods use a microwave having a wavelength of 2.45 GHz and a static magnetic field having a field intensity of 875 Gs. Accordingly, when the density of a plasma produced by the application of microwave power reaches 7.4.times.10.sup.10 /cm.sup.3, the left-hand circularly polarized wave (L-wave) of the microwave is cut off; and, when the microwave power is further increased, the right-hand circularly polarized wave (R-wave) increases the density of the plasma to 10.sup.11 /cm.sup.3 or above. When the density of the plasma is increased by increasing the microwave power, the density of the plasma increases stepwise, instead of increasing continuously (J. Vac. Sci. Technol. B, Vol. 9, No. 2, Mar/Apr, pp. 339-347 (1991)).
According to the above mentioned literature, the mode of the plasma jumps from a low mode, in which the density is 5.times.10.sup.10 /cm.sup.3 to a high mode, in which the density is 5.times.10.sup.11 /cm.sup.3, when the plasma is produced by using a microwave of 2.45 GHz.